Periodic circuit maker for electric ovens



June 24, 1930. c. WILHJELM 1,767,636

PERIODIC CIRCUIT MAKER FOR ELECTRIC OVENS Filed Nov. 15, 1927 June 24,1930 manual, PHILADELPHIA, rmmvmu PERIODIC cmcu 1'1 II'OB ELMO ovims'Applicatioa mu mm... 15, 1021. mm I0. mass.

This invention relates to temperature control apparatus for electricovens and furnaces. The object of the invention is to provide a controlapparatus of simple efiicient 6 design and construction, and eitherentirely automatic in response to temperature changes within the oven,or operable as an improved manually regulated apparatus.

With this object in view my invention is 10 embodied in an apparatus ashereinafter more fully explained and as illustrated in the accompanyingdrawing in which Figure 1 is a diagrammatic view of an elec tric ovenequipped with a temperature control apparatus embodying the invention.

Figure 2 is a plan view of the apparatus with parts omitted and brokenaway.

Figure 3 shows a modification of the contact operating cam.

Referring to the drawing the reference numeral 3 denotes an electricoven having the heating element 4 suitably connected in the main heatingcircuit comprising the line wires 5 and 6, and the connecting wires 7and 8.

The numeral 9 denotes a relay in the main heating circuit for openingand closin the latter in a well knownmanner. The rei ay is included inthe relay circuit comprising the line wires 5 and 6, connecting wires 10and 11 and contact elements 12 and 13 which are normally broken. Thecontact elements carry suitable contacts 14 and 15, one of which or bothmay be adjustable.

Means are provided for automatically clos-' ing the relay circuit toenergize the relay so as to close the main heating circuit for apredetermined period of time during a given time interval. During suchperiod the full current load will pass through the heating element inthe oven.

As one embodiment of my invention, one of the contact elements 12 and 13carry a tooth 16 or other like member of nonconducti-ng material adaptedto contact with a timing cam 17 whereby to close the'rela'y circuit atthe contacts 14 and in an obvious manner.

The timing cam is mounted on a shaft 18 operated through a reducinggearing 19 from a small electric motor 20 connected to the line in theusual manner. The motor and its operating parts are enclosed within asuitable housing 21. It is obvious that when the cam 17 is rotated, therelay circuit will be closed once to each revolution of the cam and thefull 66 current load pass through the heating element 4.

Means are provided for adjusting the position of the contact elementswith relation to v the cam in such a manner that minute adjustmentmay bemade. To this end the contact elements are suitably mounted in a blockor support 22 of nonconducting material and pivoted at 23 on a stand 24.An arm 25 is fast on the support 22 and extends to one side of the pivot23. The arm is held by a spring 26 on an eccentric 27 fast on anadjusting shaft 28 suitably supported in a stand 29.

A casing may be rovided to enclose the entire apparatus an is indicatedat 30 in Figure 2. The shaft 28 extends through the casing and isprovided with a knob 31 on the outside. 32 is a friction device formaintaining the shaft 28 in adjusted position in a well known manner.

In operation the cam 17 is timed by selecting a suitable motor andproviding the proper reducing gearing to rotate at a given speed, forinstance once in every minute. Consequently, once in every minute therelay circuit will be closed by the contacts 14 and 15 for a givenperiod depending upon the length of the efiectivecam surface and theposition, that is nearness, of the contacts to the cam.

The length of the efiective cam surface is designed to suit the localcondition and the distance of the contact from the cam may be minutelyadjusted to suit the oven requirements by rotating the eccentric 27 toraise or lower the arm 25 and thus lower or raise the contacts.

The closer the contacts are to the cam, the longer the period duringwhich the relay is energized and the heating circuit closed, and viceversa.

The requirements of the oven being known,

it is an easy matter to adjust and set the shaft 28 to accuratelyposition the contact elements accordingly. The apparatus provides sucheasy and minute adjustment that the full load from the line ma be sentthrough the heating coil either stea ily or for such period of time thatthe temperature in the oven will 5 var little if any from the desiredconstant.

hould the temperature drop, the apparatus may be instantly andaccurately set to increase the frequencies and durations of full loadimpulses in the heating circuit, and vice versa.

This invention, therefore, provides for automatically maintaining aconstant temperature under constant working condition, coupled with theadvantages of minute adjustments as the local conditions may require.

The apparatus is very simple and economical in construction andoperation. An added factor of adjustability may be introduced by usingan adjustable cam 35 on a disk 34 to be mounted on the shaft 18.

It is a distinguishing feature of this invention that no current iswasted in the operation thereof. The motor is very small and consumesvery little current. Likewise, the

operation of the relay is inexpensive.

The disclosure herein is illustrative onl Changes and modifications mareadily e made within the rinciple, of t e invention and the scope oftiie appended claim.

3G I claim:

An electric circuit closing device comprising a support, a memberpivoted thereon a pair of normally open contacts carried by said memberto the one side of the ivot, an

35 arm on said member extendin to t e opposite side of the pivot, amotor riven cam for closing said contacts at regular intervals, aneccentric in engagement with said arm and means for adjusting theeccentric to regulate the position of the said contacts with respect tothe said cam.

CHRISTIAN WILHJ ELM.

